In terms of personal computers this isn't going to mean much probably by the time it happens. The problem is that there are many, many embedded devices out in the field that are still running with 32-bit time_t vars. Example from a previous job of mine: we made building automation controllers. Those are all devices that are still out in the field and they are all still running old code. Assuming the devices don't die before the time rollover or are not replaced with newer pieces of hardware then it might become a problem.